SCREW AND METHOD FOR READING A SCREW TIGHTENING FORCE

Abstract

Provided is a screw that includes a threaded shank extending along a longitudinal axis; a head configured to be engaged by a tightening tool to tighten the screw; and an extensometer housed in a longitudinal cavity made in the shank, to measure a measurement parameter representing a tightening force of the screw. A coil, a power supply, a microprocessor and a transmitter are located in a housing made in the head. The power supply is connected to the coil to receive electrical energy by electromagnetic induction through a contactless transmission line, and to the microprocessor and extensometer to supply them with electric power. The microprocessor is connected through a conditioning module to the extensometer to receive the measurement parameter and to the transmitter to transmit the measurement parameter externally of the screw through a wireless measurement signal.

Claims

1. A screw comprising: a threaded shank extending along a longitudinal axis; a head engageable by a tightening tool to tighten the screw; an extensometer connected to the shank, to measure a measurement parameter representing a tightening force of the screw; and a coil, a power supply, a microprocessor and a transmitter, all located in a housing made in the head, wherein the power supply is connected to the coil, to receive electrical energy by electromagnetic induction through a contactless transmission line, and the power supply is connected to the microprocessor and to the extensometer to supply the microprocessor and the extensometer with electric power, and wherein the microprocessor is connected to the extensometer to receive the measurement parameter measured by the extensometer and is connected to the transmitter to transmit the measurement parameter externally of the screw through a wireless measurement signal.

2. The screw according to claim 1, wherein the coil is a coil printed on a multilayer substrate.

3. The screw according to claim 1, wherein the power supply and the microprocessor are integrated in an electronic card which is located between the coil and the extensometer along the longitudinal axis.

4. The screw according to claim 1 further comprising a conditioning module, located in the housing, interposed between the extensometer and the microprocessor and having a circuit which acts in conjunction with the extensometer to define a bridge detector, and an amplifier stage interposed between the bridge detector and the microprocessor.

5. The screw according to claim 1 further comprising a capacitor connected in parallel to the coil to define therewith a resonant circuit at a predetermined frequency.

6. The screw according to claim 1, wherein the power supply has a first and a second operating configuration, the power supply being in the first operating configuration when current is flowing in the coil, induced by a magnetic field, and in the second operating configuration when there are no currents induced by magnetic fields in the coil, and wherein the microprocessor is programmed to read the value of the tightening force and to transmit the wireless measurement signal in response to a switch of the power supply from the second to the first operating configuration.

7. The screw according to claim 1, wherein the microprocessor is programmed to generate a drive signal for driving the transmitter, and wherein the transmitter is configured to generate in the coil, in response to the drive signal received from the microprocessor, a transmission current which is variable according to a curve representing the measurement parameter measured, in order to generate the wireless measurement signal by electromagnetic induction through the coil.

8. The screw according to claim 1, wherein the power supply comprises: a first power supply element connected to the coil to receive a first supply current and connected to the microprocessor to power the microprocessor; a second power supply element connected to the coil to receive a second supply current, distinct from the first supply current, and connected to the coil through a changeover switch acting in conjunction with the second power supply element to define the transmitter, to transmit to the coil a transmission current which is variable according to a curve representing the measurement parameter measured, in order to generate the wireless measurement signal by electromagnetic induction through the coil, wherein the microprocessor is connected to the changeover switch to drive the changeover switch through a drive signal.

9. The screw according to claim 8, wherein the changeover switch is movable, as a function of the drive signal, between: a first operating state, in which the changeover switch connects the coil to the second power supply element; a second operating state in which the changeover switch connects the coil to earth; and a third operating state in which the changeover switch disconnects the coil both from the second power supply element and from earth and leaves the coil floating.

10. A wireless system for reading a tightening force of a screw applied to a structure, comprising: an extensometer connected to a shank of the screw, configured to measure a measurement parameter representing a tightening force of the screw; a coil, a power supply, a microprocessor and a transmitter, all located in a housing made in the screw, wherein the power supply is connected to the coil, to receive electrical energy and to the microprocessor and the extensometer to supply the coil and the microprocessor with electric power, and wherein the microprocessor is connected to the extensometer to receive the measurement parameter measured by the extensometer and is connected to the transmitter to transmit the measurement parameter externally of the screw through a wireless measurement signal; and a reading device having a receiver, an electrical energy source, a processor and a winding, wherein the processor is programmed to generate a primary supply current in the winding to generate a magnetic field and induce a secondary supply current in the coil of the screw, thereby transmitting electrical energy to the power supply of the screw through a contactless transmission line, and wherein the receiver is configured to detect the wireless measurement signal generated by the microprocessor of the screw and the processor of the reading device is programmed to process the wireless measurement signal to acquire the measurement parameter.

11. A method for reading a tightening force of a screw applied to a structure, comprising: measuring a measurement parameter representing a tightening force of the screw, by means of an extensometer connected to a shank of the screw; preparing a reading device having a receiver, an electrical energy source, a processor and a winding; preparing, in a housing made in the screw, a coil, a power supply, a microprocessor and a transmitter; moving the reading device close to the screw until the winding of the reading device is magnetically coupled to the coil of the screw; electrically energizing the power supply and the microprocessor of the screw, by transmitting electrical energy from the reading device through the contactless transmission line defined by the winding of the reading device magnetically coupled to the coil of the screw; acquiring, by means of the microprocessor of the screw, the measurement parameter measured by the extensometer; transmitting the measurement parameter to the receiver of the reading device through a wireless measurement signal by the transmitter of the screw driven by the microprocessor; processing the wireless measurement signal by means of the processor of the reading device in order to acquire the measurement parameter.

12. The method according to claim 11, wherein acquiring the measurement parameter measured by the extensometer is started by the microprocessor of the screw when the microprocessor detects the electrical powering step.

13. The method according to claim 11, wherein transmitting the measurement parameter through the wireless measurement signal from the microprocessor of the screw to the reading device, occurs, alternatively: i) through the contactless transmission line defined by the winding of the reading device magnetically coupled to the coil of the screw during a pause in the step of electrically energizing the power supply of the screw by means of the reading device; and ii) through a further contactless transmission line at least partly concurrently with electrically energizing the power supply of the screw by means of the reading device.

14. A method for processing a screw having an elongate threaded shank extending along a longitudinal axis and a head which can be engaged by a tightening tool for tightening the screw, wherein the method comprises: stably connecting an extensometer, designed to measure a measurement parameter representing a tightening force of the screw, to the shank of the screw; removing material from the head of the screw to form a housing accessible from an outside of the screw, lengthways from a direction opposite the shank; placing a coil, a power supply, a microprocessor and a transmitter inside the housing; electrically connecting the coil to the power supply, the power supply to the microprocessor and to the extensometer, and the microprocessor to the extensometer; and programming the microprocessor to transmit the measurement parameter externally of the screw through a wireless measurement signal.

15. The processing method according to claim 14, wherein connecting the extensometer to the shank of the screw comprises inserting the extensometer in a longitudinal cavity made in the shank of the screw.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0100] These and other features of the invention will become more apparent from the following detailed description of a preferred, non-limiting embodiment of it, with reference to the accompanying drawings, in which:

[0101] FIG. 1 shows a screw according to the invention in an exploded view partly in cross section;

[0102] FIG. 2 shows a system for reading a tightening force of a screw, comprising the screw of FIG. 1 and a reading device;

[0103] FIG. 3 illustrates the screw of FIG. 1 in a cross section through a longitudinal plane;

[0104] FIG. 4 shows the system of FIG. 2, schematically illustrating a measuring circuit of the screw;

[0105] FIG. 5 shows the measuring circuit of FIG. 4 in more detail;

[0106] FIG. 6 shows a functional diagram of a conditioning unit forming part of the circuit of FIG. 5;

[0107] FIG. 7 shows a functional diagram of a power supply forming part of the circuit of FIG. 5;

[0108] FIG. 8 shows a functional diagram of the reading device of FIG. 2.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

[0109] The numeral 1 in the drawings denotes a screw according to this invention.

[0110] The screw 1 has a shank 101 and a head 102. The shank 101 is threaded. The head 102 is designed to be engaged by a tightening (or screwing) tool such as, for example, a spanner, pliers or other tool.

[0111] It should be noted that the screw 1 constitutes a bolt (when coupled to a nut) and this description of a screw also applies to a bolt.

[0112] The screw 1 defines a longitudinal axis 103.

[0113] The shank 101 is elongate and extends along the longitudinal axis 103.

[0114] The screw internally defines a cavity 104. Preferably, the cavity 104 is elongate and extends in the longitudinal direction (parallel to the longitudinal axis 103). Preferably, the cavity 104 is positioned along the longitudinal axis 103.

[0115] In the example illustrated, the cavity 104 is accessible from the top 105 of the head 102, the top 105 constituting an end of the screw 1 opposite the shank 101.

[0116] Preferably, the cavity 104 extends at least partly inside the shank 101.

[0117] The screw 1 comprises a measuring element configured to measure a measurement parameter representing a state of tension of the screw (and hence representing a tightening force of the screw).

[0118] The measuring element is located in the cavity 104. Preferably, the measuring element is an extensometer 106. Hereinafter in this description, and without losing in generality, reference is made to the extensometer 106.

[0119] The extensometer 106 is connected (for example, glued) to the body of the screw and is configured to vary its length as a function of the length of the screw 1, with reference, in particular, to the shank 101 of the screw 1. Preferably, therefore, the extensometer 106 is located in the cavity 105 inside the shank 101 of the screw 1.

[0120] According to technology of essentially known type, the extensometer 106 is configured to generate an electrical signal representing its elongation, or length, when current passes through it. For example, the extensometer 106 comprises an electrical lead wire having a longitudinal extension whose resistance varies as a function of the length of the extensometer itself and hence of the screw it is fixed to.

[0121] The screw 1 defines a housing 107. For example, the housing 107 consists of a blind hole accessible from the outside of the screw. The housing 107 (or at least part of it) is preferably made in the head 102 of the screw 1.

[0122] In an example embodiment, the housing 107 is located along the longitudinal axis 103. Preferably, the housing 107 is longitudinally aligned with the cavity 104 and hence defines an extension of the cavity 104 as far as the top 105 of the head 102 of the screw 1.

[0123] The screw 1 also comprises a measuring unit 2, located inside the screw and connected thereto. The measuring unit 2 is preferably located in the housing 107.

[0124] The measuring unit 2 comprises a coil 3. The coil 3 is adapted to generate a magnetic field when an electric current passes through it. The coil 3 defines at least one loop, preferably a plurality of loops.

[0125] It should be noted that the extensometer 106 is functionally part of the measuring unit 2.

[0126] Preferably, the coil 3 is located in the housing 107 and is wound around the longitudinal axis 103.

[0127] In an example embodiment, the coil 3 is preferably a coil printed on a multilayer substrate.

[0128] The measuring unit 2 also comprises a power supply 4. The power supply 4 is an electronic unit designed to receive electrical energy, store it temporarily and release it to feed a load.

[0129] It should be noted that the screw 1 does not comprise batteries or other devices for generating electrical energy for long periods without in turn being fed.

[0130] The power supply 4 is configured to store electrical energy and to feed the load, without itself being fed, for a certain time interval, where the time interval is preferably not greater than (i.e., is less than) 500 ms; more preferably, not greater than 100 ms (so as to limit the dimensions of the power supply). It should also be noted that the power supply 4 is configured to deliver a current which is, preferably, greater than 5 mA, and more preferably, greater than 7 mA. For example, the current delivered is between 7 and 8 mA.

[0131] The measuring unit 2 also comprises a microprocessor 5.

[0132] Preferably, the microprocessor 5 has a memory. The microprocessor might also be made using Field Programmable Gate Arrays (FPGA) or similar technologies which perform the same functions repetitively. In an example embodiment, the microprocessor has a first, a second and a third memory. The first memory is a flash memory containing a work programthat is to say, the sequence of instructions it must perform when energized. The second memory is a RAM configured to perform processes at high speed. The third memory is a memory in which to load the data that may be necessary during processing (for example an EEPROM). Like the first memory, the third memory stores data even when the microprocessor is switched off (non-volatile memory). For example, the third memory contains a sequence number which identifies the production batch, readable together with the mechanical tension value, the nominal tension value which the screw can be subjected to, and if necessary, recommended maximum and minimum values which, when measured, may advise the operator to take steps to restore the correct value or even substitute the screw.

[0133] The measuring unit 2 also defines a transmitter. The transmitter is an assembly of electric or electronic components configured to generate a wireless signal and to transmit the wireless signal to the outside of the screw 1.

[0134] In an example embodiment, the power supply 4 and the microprocessor 5 (and the transmitter) are integrated in an electronic card 201.

[0135] Preferably, the electronic card 201 is a multilayer card, with components mounted on both sides of it (top and underside).

[0136] In one embodiment, the coil 3 might also be integrated in the electronic card 201.

[0137] The electronic card 201 is located in the housing 107. Preferably, the electronic card 201 is located under or inside the coil 3. The coil 3 is located in the housing 107 at the end of the screw 1 (that is, at the top 105 of the head 102).

[0138] Thus, the power supply 4, the microprocessor 5 and the transmitter are located in the housing 107.

[0139] The power supply 4 is connected to the coil 3 to receive electrical energy (from the coil 3) by electromagnetic induction through a contactless transmission line 7.

[0140] The power supply 4 is also connected to the microprocessor 5 to supply it with electric power.

[0141] Preferably, the power supply 4 is also connected to the extensometer 106 to electrically energize it.

[0142] The microprocessor 5 is connected to the extensometer 106 to receive the measurement parameter measured by the extensometer 106.

[0143] The microprocessor 5 is also connected to the transmitter to transmit the measurement parameter to the outside of the screw through a wireless measurement signal.

[0144] The screw 1 also comprises a conditioning module 6. The conditioning module 6 is an electronic appliance or an assembly of electronic components configured to process and/or condition a signal.

[0145] The conditioning module 6 forms part of the measuring unit 2 and, preferably, is integrated in the electronic card 201.

[0146] The conditioning module 6 is located in the housing 107.

[0147] From the a functional viewpoint, that is, in terms of electrical connection, the conditioning module 6 is (operatively) interposed between the extensometer 106 and the microprocessor 5.

[0148] The conditioning module 6 has a circuit (which defines a sensor, that is, a detector means) acting in conjunction with the extensometer 106 to measure the measurement parameter. In an example embodiment, the circuit is a bridge detector 601 of which the extensometer 106 is one side. Preferably, the bridge detector 601 is a Wheatston bridge.

[0149] The conditioning module 6 also has an amplifier stage 602, interposed between the sensor (in the example described above, the bridge detector 601) and the microprocessor 5.

[0150] In an example embodiment, the amplifier stage 602 of the conditioning module 6 comprises an amplifying element 603 (for example, a variable gain amplifier) designed to amplify an analogue signal, and an analogue-to-digital converter 604.

[0151] The numeral 605 in the drawings denotes a voltage regulator or stabilizer. As regards the power supply 4, attention is also drawn to the following. In an example embodiment, the power supply 4 comprises a capacitor (not illustrated) connected to the coil 3 to define therewith a resonant circuit at a predetermined frequency. Preferably, the capacitor is connected to the coil 3 in parallel (to define a parallel resonant circuit).

[0152] In an example embodiment, the power supply 4 comprises a first power supply element 401 and a second power supply element 402. The first power supply element 401 and the second power supply element 402 are electrically connected in parallel and are designed to operate independently of one another.

[0153] The first power supply element 401 is connected to the coil 3 to receive a first supply current. The first power supply element 401 is connected to the microprocessor 5 to supply it with electric power.

[0154] The second power supply element 402 is connected to the coil 3 to receive a second supply current. Preferably, the second supply current is distinct from the first supply current. In an example embodiment, the coil 3 is connected to the first power supply element 401 and to the second power supply element 402 through a (current) divider element 403, for example a diode divider.

[0155] In an example embodiment, the second power supply element 402 is connected to the coil 3 through a changeover switch 404. The changeover switch 404 is designed to generate a square wave to be fed to the coil 3. The changeover switch 404 cooperates with the second power supply element 402 to define the transmitter. In effect, the function of the changeover switch 404 is to generate and cause to circulate in (or transmit to) the coil 3 a variable transmission current (for example, a square wave). The transmission current is variable according to a curve representing the measurement parameter measured, in order to generate the wireless measurement signal by electromagnetic induction through the coil.

[0156] The transmission current curve generated by the changeover switch 404 is determined by a drive current generated by the microprocessor 5 and transmitted to the changeover switch 404 itself.

[0157] In effect, the microprocessor 5 is connected to the changeover switch 404 to drive it through the drive signal.

[0158] In the embodiment illustrated, therefore, the power supply 4, the processor 5 and the coil 3 together define the transmitter. Alternatively (or in addition), the measuring unit 2 (or the screw 1) might comprise a transmitter which is independent of the coil 3for example, a radio frequency transmitter of essentially known type.

[0159] More in general, several technical solutions can be adopted to transmit the measuring signal from the measuring unit 2 of the screw 1 to the outside. In one possible solution, optical transmission (an optical transmitter) is used. Such a system might, however, prove sensitive to dirt and grime, such as dust and oil, for example.

[0160] Another possible solution involves using an electromagnetic wave transmitter on frequencies typical of RFID, such as 13.6 MHz, or even higher frequencies such as industrial scientific medical (ISM) bands, such as, for example, 433 MHz, 868 MHz, 2.4 GHz (band centre values given by way of example).

[0161] Returning to the solution where the coil 3 is used both to energize the measuring unit 2 and to transfer the measurement signal, attention is also drawn to the following.

[0162] The power supply 4 has a first and a second operating configuration, depending on whether or not it receives electric power from the outside. In other words, the power supply 4 is in the first operating configuration when current is flowing in the coil 3 (induced by a magnetic field) and in the second operating configuration when there are no currents induced by magnetic fields in the coil 3.

[0163] The microprocessor 5 is configured to detectthat is, sensethe operating configuration of the power supply 4. The microprocessor 5 is programmed to read the measurement parameter (and hence to then transmit the wireless measurement signal) in response to a switch of the power supply from the second to the first operating configuration.

[0164] In practice, the power supply 4 defines a control circuit of the coil 3. This control circuit of the coil 3 is configured to receive (during a procedure for reading the measurement parameter of the screw 1) outside-induced electrical energy, in particular induced by a reading device 8, through a magnetic field which is coupled with the coil 3.

[0165] At predetermined intervals, energy transmission is purposely interrupted so that the screw with the stored energy can transmit the measurement parameter back.

[0166] The microprocessor 5 of the screw 1 thus detects, or senses, a condition in which the supply voltage present in the power supply 4 decreases, thereby inferring that the reading device 8, at that moment, is no longer transmitting energy. After a certain length of time, also predetermined, the screw 1 sends back the measurement signal representing the mechanical tension the screw is subjected to.

[0167] The energy from the coil 3 reaches two separate capacitors (that is, the first and second power supply elements 401 and 402, which constitute two separate energy stores) which are charged independently. When the power supply from the reading device 8 is interrupted, digital controls (for example, mosfet switches) configured to generate the drive signal of the changeover switch 404 enable the microprocessor 5 to detect the changeover to the coil 3 of the energy accumulated in the second power supply element 402 in order to transmit the measurement signal through the coil 3. In this example embodiment, therefore, the screw 1 causes the measurement parameter to be transmitted to the outside (to the reading device 8) in digital format (current pulses on the coil 3 which generate a magnetic field concatenated with a winding 801 of the reading device 8). This guarantees energy for the microprocessor during transmission of the measurement signal, which in any case causes a progressive drop in the energy accumulated in the second power supply element 402 and allows the same wireless transmission line 7 to be used both to energize the measuring unit 2 of the screw 1 and to transmit the measurement signal from the screw 1 to the outside.

[0168] The changeover switch 404 is shown schematically as a single switch but consists preferably of a plurality of switches, for example mosfet transistors.

[0169] Whatever the case, the changeover switch 404 is preferably movable, as a function of the drive signal, between a first operating state, in which it connects the coil to the second power supply element, a second operating state, in which it connects the coil to earth, and a third operating state, in which it disconnects the coil both from the second power supply element and from earth and leaves it floating. In the step of energizing the measuring unit 2 from the outside, the changeover switch 404 is kept in the third operating state by the processor 5. The first two operating states, on the other hand, are used to generate the square wave signal to be made to circulate in the coil in order to generate the measurement signal to be transmitted.

[0170] This description thus also provides a wireless system for reading a tightening force of a screw 1 applied to a structure and comprising the screw 1 and the reading device 8.

[0171] This description therefore also provides the reading device 8, for which protection independent of the screw 1 is claimed.

[0172] The reading device 8 comprises the winding 801, configured to generate a magnetic field when a current flows through it. In parallel (or, alternatively, in series) with the winding 801 there is a capacitor 807, configured to define with the winding 801 a resonant circuit at the predetermined frequency.

[0173] The reading device 8 also comprises a receiver 802, an electrical energy source 803 and a processor 804.

[0174] The processor 804 is programmed to generate a primary supply current in the winding 801 to generate a magnetic field and induce a secondary supply current in the coil 3 of the screw 1. That way, electrical energy can be transmitted to the power supply 4 of the screw 1 through the contactless transmission line 7. In an example embodiment, the transfer of energy occurs through a generator element 806 connected to and interposed between, the processor 804 and the winding 801. For example, the generator element 806 is an H bridge (DMOS Full Bridge). The H bridge, suitably controlled by the processor 804, sends an alternating current to the winding 801 of the coil 3 of the screw, at the predetermined resonance frequency.

[0175] The receiver 802 is configured to detect the wireless measurement signal generated by the microprocessor 5 of the screw 1. The processor 804 is programmed to process the wireless measurement signal to acquire the measurement parameter.

[0176] The reading device 8 also comprises a memory to store the data acquired (through the receiver 802 and the processor 804).

[0177] In an example embodiment, the reading device 8 also comprises a pushbutton 805 connected to the processor 804 to manually control the power supply of the winding 801.

[0178] Preferably, the reading device 8 has a handgrip 808 which can be held by the user in one hand in order to manipulate and direct the reading device 8. Preferably, the pushbutton 805 is located at a position where it can be pressed using the same hand as that holding the handgrip 808.

[0179] The reading device 8 preferably also has a display screen 807 on which the data acquired is displayed.

[0180] This description also provides a method for reading a tightening force (that is, a state of tension, or tensile tension) of a screw applied to a structure. Operatively, the method comprises the following steps.

[0181] A reading device 8 is positioned with a portion of it aligned with the longitudinal axis 103 of the screw 1. More specifically, the reading device 8 is positioned with its winding 801 facing the coil 3 of the screw 1 (and coaxial with the longitudinal axis 103 of the screw 1).

[0182] The reading device 8 is activated (for example by pressing the pushbutton 805) to generate a current circulating in the winding 801. Preferably, this current circulates in a resonant circuit defined by the winding 801. The current is variable (for example, square wave current) preferably at the resonance frequency of the resonant circuit.

[0183] The current circulating in the winding 801 of the reading device 8 thus induces, by magnetic coupling, a corresponding current in the coil 3 of the screw, thereby feeding the power supply 4 of the screw 1.

[0184] This causes the power supply 4 to change over from the second to the first operating configuration.

[0185] The processor 5 of the screw is fed by the power supply 4. Also, preferably, the processor 5 senses that the power supply 4 has changed over from the second to the first operating configuration.

[0186] In an example embodiment, the conditioning module 6 is also fed by the power supply 4 and current is made to flow through the extensometer 106 (more in general, current is made to flow through the bridge detector 601). The processor, (preferably in response to detection of the changeover of the power supply 4 from the second to the first operating configuration) acquires the measurement parameter (for example, the resistance value provided by the bridge detector 601 or a data item processed from this value).

[0187] The processor 5 drives the transmitter of the screw to transmit the measurement parameter to the outside, preferably to the reading device 8. In an example embodiment, the processor 5 detects a changeover of the power supply 4 from the first to the second operating configuration caused by an interruption in the power supply by the reading device 8) and, as a result, that is, in response to such detection, drives the changeover switch 404 energized by the power supply 4 to generate a variable electric current in the coil 3, this current (for example, a square wave at the predetermined resonance frequency) represents the measurement parameter.

[0188] That way, the screw 1 generates a wireless measurement signal which is detected by the receiver 802 of the reading device 8 by means of an induced current in the winding 801 of the reading device 8 magnetically coupled to the coil 3 of the screw 1.

[0189] The reading device 8 acquires the measurement parameter by processing the measurement signal received from the screw 1, stores it in the memory and/or displays it on the screen 807.